Other files

Changes for version 2.24

Rewrite scripts/extract.output.formats.pl, which used to download a page of documentation from graphviz.org, and parse it to build a list of output formats. The problems are: (1) Forgetting to run the script; (2) the on-line docs being out-of-date. So, as of this version, I now parse the output of 'dot -T?', which will not just be more accurate, but will also include the formats supported by locally-installed plugins. It's a win-win result.